In recent years, in order to write data which are subjected to digital signal treatment, an electrophotographic image forming method has increasingly been employed in which an organic photoreceptor is subjected to dot light exposure to form an electrostatic latent image followed by forming an image employing reversal development.
It is required that a photoreceptor, which is employed in such a method, is stable over an extended period of time and also suitable for writing requiring high resolution. Generally, compared to inorganic photoreceptors, organic photoreceptors readily respond to various types of exposure light sources because the selection range of materials for said organic photoconductors is wider. In addition, the electric potential of organic photoconductors is more stable. Accordingly, techniques employing organic photoconductors have been inevitable, especially for a process which is required for high image quality. Specifically, as charge generating materials which are required to obtain an electrophotographic photoreceptor which exhibits high sensitivity in the long wavelength region which is capable of corresponding to semiconductor laser as well as LED which have been increasingly employed, and excellent durability, phthalocyanines as well as perylenes exhibit excellent properties.
On the other hand, the strength of organic photoconductors is low. Due to that, a photosensitive layer comprised of organic photoconductors is likely to suffer problems due to abrasion wear and scratches, and enhancement of the durability has been sought. As a method to overcome such a problem, considered is a combination of phthalocyanine or perylene, which exhibits high sensitivity in the long wavelength region, as well as excellent stability of electric potential with a surface layer which itself exhibits excellent strength.
However, when the aforementioned combination is applied to a photoreceptor comprised of phthalocyanine, a problem occurs in which interference fringes, due to laser beam exposure, tends to appear on the resultant images. It is thus necessary to solve this problem.
Further, a surface layer is required which can maintain the high sensitivity as well as electric potential properties of phthalocyanine as well as perylene. For instance, in these photosensitive layers, the efficiency of carrier generation for variation in the thickness of the photosensitive layer largely depends on the strength of the electric field and the layer abrasion wear results in large variation in sensitivity. Specifically, when the abrasion wear is extensive, charging properties as well as light decay properties are greatly affected. When the charge potential is lowered, background stain is formed, while when the light decay is not sufficient, problems, such as an decrease in density and the like, occur.
Consequently, a layer structure is required which exhibits high sensitivity, and further, can maintain and stabilize the resulting high sensitivity.